In the world of data communications, communications networks provide the connections necessary to link together communications nodes located anywhere in the world. Each communications node generally provides multiple connections thereby allowing multiple users to connect to the same communications node. A communications node typically includes a remote access server such as router or an integrated services digital network (ISDN) switch to allow remote connection to the node. A communications network, known as the "network cloud" that is capable of covering a geographical area ranging from a few miles to thousands of miles, couples the remote access server to individual users.
Prior Art FIG. 1 is a block diagram illustrating a communications network connection. At one end of the communications network connection is remote access server 100. Remote access server 100 typically includes serial I/O (SIO) controller 105. SIO controller 105 interfaces with network cloud 102 through modem bank 101. Modem bank 101 consists of multiple U and/or S/T interface chips which take a network connection such as an ISDN connection and converts the ISDN connection into a standard four-wire computer communications interface. In turn, network cloud 102 provides connections to individual users 103 and 104.
For ISDN connections, the interface standard for a connection between an SIO controller and a modem bank is either general circuit interface (GCI) or interchip digital link (IDL). In both GCI and IDL interface standards, an ISDN frame is composed of serialized digital signals which are categorized as individual sub-functions/channels such as B1, B2, D, and etc.
Referring now to Prior Art FIG. 2 in which an exemplary format of ISDN frame 200 using GCI interface standard is shown. As illustrated, ISDN frame 200 using GCI interface standard consists of B1, B2, Monitor, D, C/I, A, and E sub-functions/channels in this sequential order. Briefly, the B1 and B2 sub-functions may carry either voice or data. The Monitor sub-function carries out-of-band channel signaling. The D sub-function is used to monitor changes in the ISDN line. The C/I sub-function carries control and indication signals. Finally, the A and E sub-functions are the acknowledgment and enable signals for handshake purposes. Each of the B1, B2, or Monitor sub-functions is eight bits wide. The D sub-function is two bits wide, the C/I function is four bits wide, and each of the A and E sub-functions is one bit-wide. The D, C/I, A, and E sub-functions make up what is known as the signaling and control octet. The bandwidth for each of the B1, B2, and Monitor sub-function is 64 Kbps. The bandwidth for the D sub-function, C/I sub-function, and combined A and E sub-functions is 16, 32, and 16 Kbps, respectively.
In the prior art, an SIO controller assigns a communications channel to each sub-function thereby making inefficient use of this scarce resource. Take, for example, the MC68360 QUICC, an SIO controller manufactured by Motorola Corporation of Schaumberg, Ill. Reference is now made to Prior Art FIG. 3 which illustrates an ISDN connection to the MC68360 QUICC chip. In Prior Art FIG. 3, an ISDN connection having IDL interface standard is provided to S/T interface chip 304. As discussed earlier, IDL serialized digital signals are categorized into B1, B2, and D sub-functions. S/T interface chip 304 routes sub-function B1 to voice compression/decompression (codec) circuit 302 and sub-functions B2+D to MC68360 QUICC SIO controller 300. More specifically, sub-functions B2+D are routed to a time slot assignment (TSA) circuit 301 which is part of MC68360 QUICC SIO controller 300. TSA circuit 301 then routes B2 sub-function and D sub-function to two different SIO ports, also known as serial communications controllers (SCC), 306 and 307. As such, TSA circuit 301 and SCCs 306 & 307 are separate from each other. As shown in Prior Art FIG. 3, a separate SIO port is used for each ISDN sub-function. Such inefficient use of SIO ports is exacerbated when multiple ISDN connections are involved. Moreover, the International Telecommunications Union (ITU) standard I.460 allows for further sub-division of B sub-functions such that a single B sub-function of 64 Kbps can be further divided into sub sub-functions of 8 Kbps increments. Therefore, as many as eight (8) separate SIO ports may be required to accommodate a single 64 Kbps B sub-function. Hence, it can be seen that conventional systems can rapidly exhaust available SIO ports. Thus, a need exists for a single SIO port which can handle multiple sub-functions of an ISDN frame.